1. Field of the Invention
The present invention relates to a collision avoidance device, especially a device for avoiding collisions with the ground. It can be applied in particular to civilian airliners. More generally, it can be applied to all aircraft that, in the course of their mission, have to come excessively close to the ground, for example when they are near mountains, or that have to maneuver in sectors of air space where they constitute a danger or are themselves in danger, for example in areas to which access is prohibited.
2. Description of the Prior Art
Devices for avoiding collision between aircraft and the ground are known. These devices are characterized chiefly by the use of radio-altimeters, computers that give the barometric height on the basis of pressure and temperature measurements and navigation means such as an inertial guidance system or a flight management system. The principle of these devices lies in making use of an altimeter height, taken with respect to the ground, and in making use of variations in radio-altimeter height or barometric height. The latter is used in particular because, as compared with altimeter height variations, it is available for great heights. These distances from the ground are compared with threshold values that themselves depend on the values of heights and the configuration of the aircraft, depending on whether its undercarriage, flaps or slats are deployed for example. When the parameters measured, the heights and the variations of heights as a function of time in particular, exceed the threshold values, an alarm is sent to the crew. However, such devices have the drawback of giving measurements that are excessively delayed with respect to the maneuvering of the aircraft, and hence of generating alarms that are often excessively delayed and prevent the crews from reacting in time. It is therefore likely that such devices will not to prevent collision. This may happen in particular when the relief takes a sudden upward turn, for example when the aircraft moves towards the side of a sharply rising mountain. Another drawback of the known devices is that they generate unwarranted alarms which are also called false alarms. These may occur for example when the aircraft are flying over low-altitude mountains with a good safety height but when rising features of the relief for example, while being harmless, cause false alarms. These drawbacks seriously reduce the credibility of these anti-collision devices.
Improvements have been made to these devices, for example by introducing databases that enable the modulation of the value of the thresholds to be taken into account as a function of the geographical position of the aircraft. These improvements are likely to reduce the false alarms. However, they require databases adapted to each type of terrain. As an extension of this latter approach, it is possible to envisage the preparation of a digital field model that would provide permanent knowledge, depending on the position of the aircraft, of the nature of the relief ahead of this aircraft. Nevertheless, the use of such a model would require a database describing the relief in a sufficiently precise way, hence a database that requires large-sized memories. In addition to this drawback, there is the need for procedures of exchange and for updating a database of this type. This complicates its use. The large number of information elements stored furthermore entails non-negligible risks of error. The performance characteristics of these devices, especially in terms of harmful alarms, is related essentially to the resolution of the database. Indeed, the uncertainty of measurement as regards the position of the aircraft must be taken into account in the computation of the alarm in order to prevent any belated alarm. This leads to a possibility of harmful alarms.
The present Applicant, in the document FR 2.697.796, has already proposed a collision-avoidance device for an aircraft that mitigates the above-mentioned drawbacks, especially by getting rid of random factors of variation in relief and by determining the position of the aircraft no longer with respect to the ground but with respect to known safety altitudes.
This document describes a collision avoidance device for an aircraft comprising means of geographical localization, means for the computation, on the basis especially of each geographical location and of safety altitudes memorized in a database, of a safety floor above which the aircraft should be located, means for predicting the air position of the aircraft between a first given instant and a second given instant and means to compare the predicted air position of the aircraft with respect to the constructed floor.
During operation, an alarm is, for example, activated as soon as the result of the comparison indicates that a predicted air position of the aircraft is below the floor.
The present invention is an improvement on the above device, enabling an increase in the resolution of the information elements used in the computation of alarms, without however increasing the volume of the database. It also makes it possible to be no longer dependent on possible errors in the measurement of navigation and thus makes it possible to cancel the risk of a belated alarm.